Comparing water filters on their product pages runs into one recurring trap: everybody advertises "removes chlorine" and "improves taste", which is about as discriminating as praising a car for having wheels. Any gram of activated carbon removes chlorine. The real differences hide in numbers the listings carefully avoid.
What I look at, in this order
Cost per gallon filtered. It is the only figure that lets you compare a pitcher, a faucet mount and an under-sink unit on the same basis. A $7 pitcher cartridge good for 40 gallons works out at 17 cents a gallon; a $20 faucet cartridge good for 100 gallons lands around 20 cents; an under-sink block rated for 1,000 gallons drops under 10 cents. The purchase price of the housing is almost incidental beside that.
What it is certified for, and under which standard. This is the criterion that actually separates products. NSF/ANSI 42 is aesthetic: chlorine, taste, odor. NSF/ANSI 53 is health: lead, cysts, certain VOCs. NSF/ANSI 58 is reverse osmosis. A filter certified 42 only is not certified for lead, no matter what the packaging photograph suggests. When no standard is named at all, assume taste and nothing else.
Real flow rate. A filter that takes thirty seconds to fill a glass ends up bypassed: the lever goes to "unfiltered" and never comes back. Above about 0.5 gpm daily use stays comfortable; the better faucet mounts do more.
Whether it fits your faucet. The number one reason these get returned. Pull-down sprayers and flat spouts refuse most screw-on filters — check before buying, not after.
One market, three logics
The legacy brands like Brita and PUR sell simplicity and cartridges available in every supermarket in the country. The under-sink specialists sell discretion and long-life cartridges, at the cost of an installation. And the pitcher sells having nothing to install at all.
| Model | Micron | Flow | Filter life | Rating | Price | |
|---|---|---|---|---|---|---|
PUR PLUS faucet mount PUR | 1 µm | 0.5 gpm | 3 mo | 4.1/5 | $34 | See price |
Waterdrop 15UB under-sink filter Waterdrop | 0.5 µm | 2 gpm | 12 mo | 4.4/5 | $109 | See price |
Brita Everyday 10-cup pitcher Brita | · | · | 2 mo | 4/5 | $39 | See price |
Prices shown are indicative · affiliate links.
That table shows the cost-per-gallon point better than any paragraph: the "Filter life" column runs from 2 months for the pitcher to 12 months for the under-sink. Divide cartridge price by capacity and the ranking inverts completely compared with purchase price. My commented selection is on the section's front page, the under-sink format has its own page in which under-sink water filter to choose, and the full match between approaches — up to reverse osmosis — is settled in reverse osmosis vs pitcher filter.
One reminder before comparing anything: none of these machines treats hardness. If that is your subject, check your hardness and read the softener section instead.
